Conventionally, most liquid fabric conditioning or fabric softener compositions make use of the thickening properties of surfactant ingredients or added salts to provide a desired rheology. More recently, the trend has been to incorporate specific thickeners into fabric softening compositions to provide a desired viscosity which remains stable over extended periods of time.
In commercial liquid fabric softener formulations the rheological properties of the product are critical for consumer acceptance. A common method of enhancing product appeal and conveying a perception of product richness and efficacy is to increase the apparent viscosity of the liquid product to a value of at least above 50 cps (as measured on a Brookfield RVT, 50 rpm, Spindle 2). Another common technique for enhancing product appeal is to modify the flow elasticity components of the liquid product so as to reduce the flow thereby rendering it more syrupy in nature while avoiding an aesthetically unpleasing stringy and non-uniform flow.
Cationic linear or cross-linked polymers are well-known in the art as ingredients to provide apparent viscosity in fabric softener compositions. However, there is no known method to modify the flow elasticity properties at a given level of viscosity insofar as flow elasticity is a function of the cationic polymer structure itself, and its level in the product composition.
Linear cationic polymers having high molecular weights are known to provide high flow elasticity to liquid fabric softeners. But, the resulting compositions are often sensitive to inorganic electrolytes and high shear resulting in liquid products which are generally unstable and separate into different phases upon aging.
In EP 394 133 (Colgate-Palmolive) there are described stable aqueous fabric softening compositions containing a di-long chain, di-short chain quaternary ammonium softening compound in combination with a fatty alcohol and a water-soluble polymer to improve the rheological properties and enhance the softening performance of the composition.
WO 90/12862 (BP Chemicals Ltd.) discloses aqueous based fabric conditioning formulations comprising a water dispersible cationic softener and as a thickener a cross-linked cationic polymer that is derivable from a water soluble cationic ethylenically unsaturated monomer or blend of monomers, which is cross-linked by 5 to 45 ppm of a cross-linking agent comprising polyethylenic functions. An example of such a cross-linking agent is methylene bis acrylamide.
In EP-A-0 799 887 (Procter & Gamble) liquid fabric softening compositions are described which are said to exhibit an excellent viscosity and phase stability as well as softness performance, which compositions comprise: (a) 0.01-10 wt. % of a fabric softener component, (b) at least 0.001% of a thickening agent selected from the group of (i) associative polymers having a hydrophilic backbone and at least two hydrophobic groups per molecule attached to the hydrophilic backbone, (ii) the cross-linked cationic polymers described in the above-mentioned WO 90/12862, cross-linked by 5-45 ppm of cross-linking agent comprising polyethylenic functions and (iii) mixtures of (i) and (ii), and (c) a component capable of sequestering metal ions.
In WO 02/057400 (Colgate-Palmolive) fabric conditioning compositions are described containing cationic polymeric thickeners obtained by polymerizing a water soluble cationic vinyl addition monomer, from 0 to 95 mole percent of acrylamide and from 70 to 300 ppm of difunctional vinyl addition monomer cross-linking agent. The thickened softening compositions are stated to be especially efficient for delivering fragrance in the softening composition to the treated fabrics.
While the use of polymeric thickeners to enhance consumer appeal is widely known in the prior art, there remains a need for liquid fabric softeners wherein the rheological properties of viscosity and flow elasticity can be modified independently of each other so as to provide an efficient method of optimizing the flow profile of the fabric softener product in response to a particular consumer preference.